In a traditional Wideband Code Division Multiple Access (WCDMA) communications network, a mobile terminal (known as a user equipment—UE) communicates wirelessly with a local base station (known as a Node B), which itself is connected to a radio network controller (RNC) that is responsible for the control of the Node Bs and that carries out radio resource management. An exemplary system is shown in FIG. 1.
One of the functions carried out by the radio network controller (RNC) is the control of the quality of the communications to and from the user equipment (UE). In particular, the respective transmission powers of the user equipment and Node B are adjusted to meet some predetermined or adjustable target value.
Uplink inner loop power control (which is also known as fast closed loop power control) is the process by which a user equipment can dynamically adjust its transmission power to an appropriate level. The Node B will measure a signal-to-interference ratio (SIR) from the signal received from the user equipment and compare this to a desired SIR value. The Node B will generate a control signal based on this comparison and transmit the signal to the user equipment. The user equipment will then adjust its transmission power in accordance with the received control signal.
Uplink outer loop power control is the process by which the radio network controller sets the desired signal-to-interference ratio for each Node B in the network. The radio network controller is aiming to maintain the quality of the communication link between the user equipment and Node B (namely a Frame Error Rate—FER), while minimising the transmission power used.
A recent development for WCDMA (and other) networks is the introduction of femtocell devices. Femtocell devices combine the elements of a Node B and radio network controller into a single device that is connected to an intranet or the Internet via an Ethernet or a broadband connection. Femtocell devices can be placed in homes or businesses and provide voice and data services to a user equipment in the same way as a normal Node B. However, femtocell devices provide enhanced coverage and capacity beyond what is normally available in such environments from the overlaying macro-cellular network.
One consequence of the reduced infrastructure is that a femtocell device is assumed not to operate in a soft handover mode (in which a user equipment can be simultaneously connected to two or more cells during a call). Any calls (whether voice or data) that are routed through the femtocell device will comprise only a single Radio Link, with no requirement for macro diversity splitting or combining in a Selector Distributer Unit (SDU) at the radio network controller.